AST parsing supports null default values on input objects

Sources/GraphQL/Utilities/ValueFromAST.swift

@@ -23,6 +23,10 @@ func valueFromAST(
     variables: [String: Map] = [:]
 ) throws -> Map {
     if let nonNull = type as? GraphQLNonNull {
+        guard !(valueAST is NullValue) else {
+            throw GraphQLError(message: "Null value provided to non-nullable type")
+        }
+
         // Note: we're not checking that the result of valueFromAST is non-null.
         // We're assuming that this query has been validated and the value used
         // here is of the correct type.
@@ -32,6 +36,10 @@ func valueFromAST(
         return try valueFromAST(valueAST: valueAST, type: nonNullType, variables: variables)
     }
 
+    guard !(valueAST is NullValue) else {
+        return .null
+    }
+
     if let variable = valueAST as? Variable {
         let variableName = variable.name.value
 

Tests/GraphQLTests/UtilitiesTests/BuildASTSchemaTests.swift

@@ -1186,4 +1186,23 @@ import Testing
         // 'mutation' operation.
         #expect(schema.mutationType == nil)
     }
+
+    @Test func supportsNullLiterals() throws {
+        let sdl = """
+        input MyInput {
+          nullLiteral: String!
+        }
+
+        type Query {
+          field(in: MyInput = null): String
+        }
+        """
+        try #expect(cycleSDL(sdl: sdl) == sdl)
+
+        let schema = try buildSchema(source: sdl)
+
+        let rootFields = try #require(schema.getType(name: "Query") as? GraphQLObjectType)
+            .getFields()
+        #expect(rootFields["field"]?.args[0].defaultValue == .null)
+    }
 }